Absorbance and optical responsivity of two-dimensional mechanical resonators at oblique incidence

Highlights: • We propose a simple method to controllably enhance the absorbance and the optical responsivity of devices based on two-dimensional mechanical resonators. • Our method consists in shining monochromatic light on the device at oblique incidence and measuring the intensity of reflected light. • For s-polarized light, absorbance and optical responsivity strongly increase with increasing incidence angle. -- Abstract: Optical reflectometry is a well known technique employed to measure the displacement response of mechanical resonators. This technique consists in shining monochromatic light on the resonator at normal incidence and measuring the intensity of reflected light. In the case of resonators fabricated from suspended membranes of two-dimensional materials, fluctuations of distance between the membrane and the underlying substrate are transduced into fluctuations of reflected light intensity. Here we consider an alternate configuration where we shine light at oblique incidence. Within the plane wave model, we calculate the absorbance of the membrane, the reflectance of the device composed of the membrane and the reflective substrate, and the optical responsivity defined as the derivative of reflectance with respect to membrane displacement. We illustrate our calculations with the example of a resonator based on monolayer molybdenum disulfide and find that these quantities can be tuned by changing the angle of incidence, especially in the case of s-polarized light. These results may serve to design experiments where the absorbance and optical responsivity of the resonator are tuned by tilting the device.